Traditional depictions of oni

Many people give the translation for "oni" as "demon", but below we examine more accurate terms for the various depictions of oni in Japanese stories. On the whole, it will be seen that a modern oni is always some kind of minor evil in the flesh that afflicts, threatens, or sometimes even ignores humans. This is in contrast to the usual use of the word "demon" in English, which refers to the fallen angels in the Bible, who are immaterial and who can possess humans. In fact, a much closer translation, looking at the Eastern depictions of an oni, would be "ogre", "beast" or "monster", but not "demon", which more closely corresponds to the Japanese word "akuma" ("evil being").

Imps

In traditional Buddhist-Japanese mythology, the oni are the exact counterparts of Christian imps (or devils with a small D). Some would guard the gates of Buddhist hell, while others would hunt down bad people and bring them to hell, and others would actually torture the bad people in hell. It's exactly what Christian imps do, so it's a pretty exact analogy. Recurrent features of oni were somewhat improbable skin color, two small horns on the forehead, a big club (imps have forks instead), and they were dressed in tiger skins. The iron club is called a kanabō.

Ghosts

Before the influence of Buddhism, oni may have been depicted as immaterial spirits like the yurei, which needed to be driven out through yin-yang magic. Instead of being the "official enforcers of the underworld", they would infest sacred places and prey on humans. However, the concept of oni eventually crystallized into a more solid form.

Ogres

The theme of the monstrous, man-like enemy that must be slain by samurai or a demon-hunter resembles Western (Greek, Medieval, Slavic) heroes and the mythological beasts they were said to have slain. As opposed to the Buddhist "imps" or the Shinto "ghosts", this is more secular mythology, closer to the fantasy genre than a moral tale belonging to religion.

[Taken from one of the stories of the demon-hunter, Raiko.] While in Kyoto, he and his five retainers heard tale of an oni that lived inside the great gate Rashoumon, the southern gate on the main road through Kyoto. One of his retainers, Watanabe, volunteers to see if this is true, and if so, slay the oni and hang a talisman with all of their names on the gate's handle. Sure enough, he encounters an oni there, but only succeeds in severing one of its arms and driving it off.

Aliens

As seen in contemporary anime, Japan's view of the oni has mellowed somewhat; oni might simply be immortal, aloof, selfish beings, superior to humans but with no clear intentions about them. In some cases they are clearly depicted like Western ogres.
Some oblivious, some malicious, some downright malevolent. Some, however, could feel sympathy or pity for the humans and defend them against a greater evil (end-of-all-worlds kind). But mostly they're just outsiders, aliens in the mortal world.

A classic modern example of oni is found in Urusei Yatsura, where Lum (pictured, below) and her relatives are aliens (literally, the alien race of Oni) sent here to (fairly benevolently) conquer Earth. Their powers include flying, breathing fire, and shocking electrically. Lum has the typical two horns of an oni, but they're mostly hidden by her hair.

Satire

Occasionally the modern take on oni is a bit more satirical, as in the case of George Saotome (pictured, below) from YuYu Hakusho, who appears to be a traditional monstrous oni in tiger skins, but who is actually a mild-mannered, harried office worker, assisting the ruler of Spirit World. In Dragon Ball Z, Goku accidentally falls into Hell and encounters Goz and Mez (pictured, below), who challenge him to physical competitions. They display the traditional red-and-blue coloring and one-and-two horns, as well as carrying kanabō.

Lum

George

Goz and Mez

Further reading

Russian meaning

In Russian, "oni" means "them". Since the title was transliterated into Cyrillic characters, some Russian gamers tend to assume that the game is actually called "Them", which just so happens to convey the same creepy ambiguity as "Oni". "Oni" also means "them" in Polish, but when released in Poland, the name was not transliterated so the same lucky effect did not occur.

Real origin of name

As explained here, "Oni" was originally going to be the game's code name during development. Brent Pease, who first formulated the idea for the game, asked for the Japanese word for "ghost", as a reference to his inspiration, Ghost in the Shell. As later explained by Hardy LeBel (the story lead) here, in writing the story he tried to incorporate the real meaning(s) of "oni" into the game. Speculation on the ways he did this are found below.

Connections to the game

Real reason for the name aside, does the name of the game manifest itself in any way within the story?

Monsters

If one searches Oni's dialog transcripts for "monster", a possible translation of "oni", there is a theme developed where Muro and his men are described by Konoko as monsters. Upon learning about the Chrysalis, she is concerned that she will become one too, and even refers to herself as a monster when speaking to an unnamed NPC. The point at which the player has to decide whether to kill Griffin contains separate "outro" lines for the murder and mercy scenarios. If she kills Griffin, Konoko calls him a monster for what he did to her. If she spares him, she says that she herself won't be "the monster you thought I would be".

Finally, though the game refers to him as Mutant Muro, Muro's transformation in the killed-Griffin scenario is certainly monstrous, and no doubt intended to reflect Konoko's own choice about Griffin's life and what that might portend for her development as a symbiote.

Red oni & blue oni

As TV Tropes explains here, oni are most often depicted as red and blue. Over time, personalities were associated with these colors and used as character tropes. While normally the red-oni character is the fiery one and the blue-oni character is the cool, collected one, this can be inverted too. It's probably worth noting here that Konoko's Daodan aura is blue and Muro's is red ;-)

Transformation through anger

As a Portuguese article states, "It is also said that a man with anger will transform in an Oni. Japanese folklore also says that a wife of great jealousy will become a Hannya, that is, a feminine Oni. [...] The Buddhist Oni is not always an evil force; in the Buddhist legends there are stories of monks who, after death, became Oni in order to protect their temples from disasters. The belief in Oni reached its zenith in the 18th and 19th centuries."

At the very least, this describes Mutant Muro well. For that matter, all the known Daodan symbiotes are violent individuals. Barabas is an elite Striker, and Mukade tempts Mai to come over to the dark side and 'embrace the oblivion'; Mai ends their fight with gratuitous violence. Kerr tells her later that her final form will be a manifestation of her true self, leaving us to wonder if her true self is naughty or nice, and what appearance this will result in.

Incidentally, mukade are large centipedes native to Japan. Pagan mythology depicts giant versions of these things alongside gods, dragons and other beasts. As opposed to e.g. dragons, the Mukade were irredeemably vile, so of all the beast-gods they're the most likely to fall in the category of oni, super-oni even... See Mukade's page for more.

Barabas

The Japanese have a saying, "oni ni kanabo", "like an oni with its iron club". The phrase conveys the concept of an already strong entity with a weapon to make it even stronger. In line with that, Barabas is already represented as a very strong fighter, and on top of that, he has the game's biggest weapon in his hands when Konoko first confronts him.

But there's more. Barabas also possesses a regenerative ability, which is an occasional attribute of oni, as well as horns, and to top it all off, he's guarding a gate, as many oni do in folk tales. Coincidence?

Miscellany

The Iron Demon is an oni, at least in name. The "Iron" may be a reference to the kanabo.

Dark Horse's comics series involves "ghosts". Thus, in episode 1, "Syndicate thieves have been spreading rumors of a ghost-like entity that attacks them after successful jobs and steals their loot". In episodes 2 and 3, "mysterious 'ghosts' are plaguing Syndicate operations, and Agent Konoko, while investigating the Syndicate, finds out what these 'ghosts' are."

Alternate universe titles for Oni

What if Brent had received an accurate response that day as to the Japanese word for "ghost"? Well, the most common words for ghost seem to be youkai, yurei, youma, and konpaku. So in an alternate universe, it could be that we're all big "Youma" fans or avid players of "Youkai".

It's probably worth pointing out here that an "ou" is one of the ways of representing the long 'o' sound in the standard Hepburn romanization system. The sound can be written as an 'o' with a macron: ō. Since most English speakers don't know the proper reading of "ou", they would be inclined to pronounce "youma" as "yuu-ma" when it should really be said "yoh-ma". So presumably Bungie would have ended up just writing it "Yoma" or "Yokai" to avoid confusion if Brent had used one of those words for the project's code name instead of "Oni".